1. Field of the Invention
Embodiments of the invention generally relate to methods and apparatus for supporting and transferring substrates and reducing pumping volume during batch processing. Embodiments of the invention also relate to methods and apparatus for uniform gas delivery and uniform heat transfer in a batch processing chamber.
2. Description of the Related Art
The effectiveness of a substrate fabrication process is often measured by two related and important factors, which are device yield and the cost of ownership (COO). These factors are important since they directly affect the cost to produce an electronic device and thus a device manufacturer's competitiveness in the market place. The COO, while affected by a number of factors, is greatly affected by the number of substrates produced per hour. Batch processing effectively improving effectively improves COO by substantially increasing the number of substrates processed without substantially increasing expenses.
The term batch processing generally indicates a process step that can process two or more substrates at one time. The advantages of batch processing are generally twofold. On the one hand, batch processing can increase system throughput by performing a process recipe step that is disproportionately long compared to other process recipe steps in a substrate processing sequence. On the other hand, in some processing steps, such as ALD and CVD, where expensive precursor materials are used, batch processing can greatly reduce usage of precursor gases compared to single substrate processing. A batch processing chamber having a large ratio of substrate surface area to chamber volume is desirable to reduce the usage of precursor gases.
Substrates are generally supported and transferred by a substrate boat during batch processing. FIG. 1 is a sectional view of a batch processing chamber 100 having a typical prior art substrate boat 101. A plurality of substrates 140 are generally placed in the substrate boat 101 on susceptors 104 which are supported by a plurality of bars 106. Each substrate 140 may rest directly on a perspective susceptor 104, or may be suspended between two susceptors 104 on three on more pins (not shown) attached to the surface of the perspective susceptor 104. The plurality of bars 106 are generally attached to a bottom plate 105 and a top plate 102. The bottom plate 105 may be generally connected to a shaft 118 which configured to convey vertical and rotary movements to the substrate boat 101. The shaft 118 is coupled to a rotary seal 107 which is positioned in a bore 109 of a seal plate 108. The seal plate 108 is configured to move vertically. When the seal plate 108 is in an upper position, as shown in FIG. 1, the substrate boat 101 is inserted into a vacuum chamber 112 formed by chamber walls 110 and the seal plate 108. When the seal plate is in a lower, the substrate boat 101 is removed from the vacuum chamber 112, not shown. The batch processing chamber 100 in FIG. 1 is shown in its processing position in which the vacuum chamber 112 is insulated. One or more inlets 122 in fluid communication with the vacuum chamber 112 are generally provided for supplying processing or carrier gas into the vacuum chamber 112. In one aspect, an injector 120 having a plurality of holes 124 may be positioned in one side of the substrate boat 101 and connected to the inlets 122. The plurality holes 124 may form a vertical shower head to evenly deliver gas up and down the vacuum chamber 112. An exhaust assembly 130 in fluid communication with an outlet 132 may be generally positioned on an opposite side from the injector 120. In one aspect, a plurality of slots corresponding to the holes 124 of the injector 120 may be formed in the exhaust assembly 130 to further facilitate horizontal flow near the surface of each substrate 140.
FIG. 2 is a perspective view of a typical prior art substrate boat 200. The substrate boat 200 may have a top plate 202, a bottom plate 205, and a plurality of support members 206 vertically extended between the top plate 202 and the bottom plate 205. In some cases, each of the plurality of support members 206 has plurality of recesses 203 configured to hold substrates therein. In other cases, each of the plurality of support members 206 generally has a plurality of support fingers 204 extended therefrom configured to support substrates 240. The support fingers 204 are generally positioned evenly on each of the plurality of the supporting member 206. The support fingers 204 with the same heights are configured to support the same substrate 204. It is also common for a substrate boat to have ring shaped susceptors which may or may not be in direct contact with substrates.
Examples of hardware and methods used to perform batch processing is further described in U.S. patent application No. 6,352,593, entitled “Mini-batch Process Chamber” filed Aug. 11, 1997, and U.S. patent application Ser. No. 60/642,877, entitled “Flexible Substrate Sequencing System Using a Bath Processing Chamber” filed Jan. 10, 2005, which are hereby incorporated by reference in their entireties.
Due to the shrinking size of semiconductor devices and the ever increasing device performance requirements, the device fabrication process now requires greater uniformity and repeatability. Uniform gas delivery and heat transfer in a batch processing chamber is more difficult to achieve than in a single substrate system. Adding susceptors to a substrate boat used in a batch processing chamber is known to promote uniform gas delivery and heat transferring. However, including susceptors usually increases the pumping volume of the chamber.
Therefore, there is a need for a system, a method and an apparatus for batch processing that meet the required device performance goals and increase the system throughput.